This invention pertains to an apparatus and method for cleaning a lens system and, in particular, the three rotating lenses of a 3-in-1 lighthouse.
In manufacturing cathode-ray tubes for use in color television, a panel assembly is formed which includes an apertured shadow mask mounted in a faceplate panel adjacent to a cathodoluminescent screen. The screen comprises a pattern of red, green and blue phosphors surrounded by a black matrix on the inside of the panel. Phosphor slurries and a black matrix application are deposited on the inner surface of the panel utilizing chemical photoresist processes which use photoresist films. The shadow mask is utilized as a photolithographic mask during steps which expose the photosensitive films to light. The light exposure steps are carried out on a photoexposure apparatus known in the art as a "lighthouse".
The lighthouse is designed to expose the photosensitive films by projecting light from a small area radiation source through the shadow mask. Beams of light pass through the apertures of the shadow mask to form a pattern, substantially of the same shape as the apertures in the mask, on the photosensitive films. The lighthouse is designed so that these beams of light follow the same trajectories through the shadow mask as will the electron beams in the finished product. Since the color cathode-ray tube uses three electron guns (one for each of the three colors red, green and blue), the lighthouse will generally have some provision for adjusting the position of the light source and adjusting the optics of the lighthouse to mimic the effect of the three different electron guns.
A 3-in-1 lighthouse is used to form the black matrix in the regions where the electron beams will not fall. In constructing the black matrix, a negative photoresist film, which hardens on exposure to ultraviolet (UV) light, is applied to the inner surface of the panel and exposed three times in the 3-in-1 lighthouse from all three color-center positions using three different trimmer lenses (one for each color) supported by a rotatable turntable. After development of the negative photoresist film, the surface contains a plurality of photoresist dots in the positions later to be openings in the matrix. Next, a water suspension of graphite is slurried on the surface and dried. An aqueous solution of hydrogen peroxide is then used to develop the matrix. The hydrogen peroxide disintegrates the photoresist dots and dislodges the overlying black layer while leaving undisturbed the graphite that is in direct contact with the glass, thereby forming the black matrix.
During the production of high-resolution display tubes, it is important that the rotating trimmer lenses in the 3-in-1 lighthouse be kept free of foreign particles during the three exposure steps. Particles on the lenses may cause an irregular transmission of UV light through the lenses, resulting in a defective black matrix pattern which is unsuitable for high-resolution display tubes. Defective matrix patterns are rejected as scrap, thereby increasing production costs. Thus, it is desirable to keep the three rotating trimmer lenses particle free.